The present invention relates to fabrics for use on papermaking machines, and more particularly to woven fabrics as used in the forming section of papermaking machines.
In the typical forming section of a papermaking machine, an aqueous suspension of paper pulp, known as "furnish", is evenly distributed onto a traveling forming fabric. The forming fabric is generally an endless, foraminous belt woven from threads of synthetic material. As the forming fabric travels through the forming section of the papermaking machine, water drains through the fabric to form a generally self-supporting continuous fiber mat or web on the fabric surface. When the fibrous web reaches the end of the forming section, it is picked up from the forming fabric and transferred to the press section of the papermaking machine, where additional water is squeezed from the web by passing it through the nips of a series of press rolls. The web is then transferred to a dryer section, where it is passed about a series of heated cylinders to evaporate still further amounts of water to yield the final paper sheet.
Forming fabrics pass over and around dewatering elements and machine rolls of the papermaking machine at high speeds and are subject to considerable abrasive wear. They must have a high resistance to such wear, and must also withstand tension loads imposed upon them as they are drawn through the paper machine without undue stretching or change in dimensional size. Forming fabrics must also provide a paper supporting surface which does not excessively mark the paper sheet, and from which the sheet may be readily released when it passes to the subsequent press section of the paper machine. The supporting surface should hold and retain the fibers with minimal loss through the fabric. Water drainage through the fabric should be uniform, and for certain paper grades the knuckle spacing and the openings in the fabric should be regular in character throughout the fabric to obtain uniformity in the paper web. Thus, a forming fabric must meet several stringent requirements concerning both its physical characteristics and its papermaking qualities.
Paperforming fabrics are normally woven from threads of synthetic material in a variety of weave patterns. Early synthetic fabrics were woven in one over-one under (1.times.1) plain weaves and one over-two under (1.times.2) semi-twill weaves in much the same fashion as metal wires which they supplemented. Subsequently, they have been commercially woven in one over-three under (1.times.3) and two over-two under (2.times.2) four harness patterns, and in one over-four under (1.times.4) and two over-three under (2.times.3) five harness patterns. There has also been some suggestion in the literature that one over-five under (1.times.5) six harness and two over-eight under (2.times.8) ten harness weaves might be employed for synthetic forming fabrics.